1. Field of the Invention
The present invention relates to a medical instrument such as an endoscope which detects, for example, a shape when the medical instrument is inserted into a subject.
2. Description of the Related Art
There is known an observation apparatus for insertion-shape of an endoscope which detects, for example, a shape when an endoscope is inserted into a subject such as a patient. This apparatus comprises a large number of transmitting coils provided in an insertion portion of the endoscope, and also comprises an antenna including a receiving coil. This apparatus transmits magnetic fields from all the transmitting coils in a time-division manner, and receives the magnetic fields by the receiving coil of the antenna, thereby detecting the positions of all the transmitting coils, and from these positions, detecting the shape of the insertion portion of the endoscope.
In Jpn. Pat. Appln. KOKAI Publication No. 2003-290129, coils C1 to C30 arranged in the insertion portion of the endoscope are classified into groups A, B, and a C, each including ten coils. The coils C1 to 010 in the group A are connected to timing circuits P1 to P10, the coils C11 to C20 in the group B are connected to timing circuits P11 to P20, and the coils C21 to C30 in the group C are connected to timing circuits P21 to P30. In Jpn. Pat. Appln. KOKAI Publication No. 2003-290129, the timing circuits P1 to P30 are connected to 10 oscillators which have different oscillating frequencies. In such a configuration, according to Jpn. Pat. Appln. KOKAI Publication No. 2003-290129, each of ten timing circuits, for example, each of the timing circuits P1 to P10, P11 to P20, and P21 to P30, . . . is intermittently turned on by coil driving timing signals INTMT01 to 30 from a control circuit 51. Thus, Jpn. Pat. Appln. KOKAI Publication No. 2003-290129 discloses that each of the coils C1 to 010, C11 to C20, and C21 to C30 belonging to each of the groups A, B, and C is sequentially and intermittently driven, so that it is possible to handle cases in which the number of coils is large.
In Jpn. Pat. Appln. KOKAI Publication No. 2003-245242, a midpoint dPmi of an arc is found by interpolation processing of detection points Pi and Pi+1 of source coils arranged in the insertion portion. When the length of the arc is substantially equal to the actual arrangement interval of the source coils, the midpoint dPmi is set as an ideal point. When the length of the arc is much smaller than the actual arrangement interval of the source coils, a point Pvi extending from a midpoint of line segments Pi and Pi+1 in a direction to connect the midpoint dPmi of the arc is set as an ideal point, and the line segments Pi and Pi+1 including the ideal point Pvi are subjected to interpolation processing. Thus, Jpn. Pat. Appln. KOKAI Publication No. 2003-245242 discloses that the shape of the insertion portion can be accurately detected as if a source coil is disposed at the ideal point.